Hoffman 7M112 tabletop
 

I must have rocks in my head. I have no place to put this mutt, and it looks desperately cheap, but it was one of those $20 craigslist rescues. A Hoffman 7M112, according to the model stamp on the back cover.

http://antiqueradio.org/art/Hoffman7...odelNumber.jpg

Sams lists nothing for that model number, but they do list a Hoffman 202, which matches the chassis number on the rear apron. By that measure, the correct Sams folder should be 205-5:

https://www.samswebsite.com/en/photo...index/id/71131

Before I spend $15 on a download, can anyone confirm that this is the correct folder? I can't read the model numbers on the tiny image of the folder's front page.

Judging by the tube lineup, this is a pretty basic TV. They didn't break the piggybank on the cabinet, which looks like thick pressboard. The bottom of the cabinet is pegboard, which --not surprisingly -- has begun to bust out along one edge. And there's a brightener on the 17HP4 picture tube (sigh).

Oh well, enough whining. I try to tell myself it's kind of cute, at least in the way that baby warthogs are cute. And I'll probably get at least $20 of enjoyment fooling around with it.

Phil Nelson
Phil's Old Radios
http://antiqueradio.org/index.html

http://antiqueradio.org/art/Hoffman7...tLookFront.jpg

http://antiqueradio.org/art/Hoffman7...stLookBack.jpg

http://antiqueradio.org/art/Hoffman7...okInterior.jpg

That's a nice clean looking set!

I have a 17LP4 in a beat up Emerson I don't really want to fix, wonder if it'll sub for the 17HP4?

A quick glance at the spec sheets suggest it might, not sure about the physical dimensions though.

Anyone have a Sub book handy?

This website shows a model 7M112B and in Sams 194 but doesn't say which folder.http://new.tvhistory.tv/search/viewp...132/era/2.html The picture looks pretty close.

That's not a bad looking set for a low line model. Looks in good shape too. I would say it's well worth $20.

Better photo of 205-5 here:
http://vintageadsandbooks.com/hoffma...l-0520505.html
jr

I'm guessing that the model shown has brightness, H and V hold on the back, where yours has 3 holes, as it appears to not have a pencil box door. :scratch2:

Phil, if you haven't already bought the download, send me your address in a PM, and I'll send out a free hardcopy to you.

.

The 17LP4 has a cylindrical faceplate, where a 17HP4 has a spherical faceplate. The 17L is a lot rarer than the 17H. :yes:

Thanks, 205-5 is definitely the right folder. Mine does have the B, H & V controls behind the (cheap!) gold plastic pencil door. Hard to tell from the Sams photo -- maybe that other model also has a pencil door, but the detail is just washed out against a lighter cabinet color.

Jim, I'll send a PM with my address. That would be great to get a copy of Sams.

Regards,

Phil Nelson

Glad to help those who help others! Thanks for the great website and all the restoration adventures.

.

I was going to make a thread about this, but I figured that I could post it here...
Does anyone know anything about the easy vision model 7B-157?

Probably should start your own thread, as Phil's Hoffman's set doesn't appear to be an Easy-Vision set, so what you are asking about doesn't fit under this topic.

.

Photofact here:
http://www.ebay.com/itm/like/3604050...ectorid=229466
Looks like a 21" version of the set Phil has.

Not affiliated,
jr

I guess so... :p
Sorry, I want attempting to hijack your thread Phil...

Well, already I got my basic question answered, so no harm done. It's usually less confusing if you don't mix up threads, though.

I was about to ask dieseljeep if he knows of any other 17" tubes that can sub for a 17HP4, when I thought to check this one, just in case. After about 90 seconds on the tester, the needle cruised up into the happy zone.

http://antiqueradio.org/art/Hoffman7M112CRTTest.jpg

It may not be the greatest tube on Planet Earth, but I'm betting it will make a picture. I'll set the brightener aside and try the set bareback when its turn comes.

Phil Nelson

Cool :) I've encountered several sets lately with brighteners on good CRTs. I'm starting to think it was a way for servicemen to make a quick buck back in the day.

The only CRT that fit, mechanically would be a 17BP4, but it is a magnetically focused CRT. You would have to furnish and mount a PM focus unit.
Good thing the CRT is good. It looks like a replacement to me.

That's typical of any C.R.T. that has sit unused for many years.. it usually takes about 15 miniutes of warmup time for it to come up to full emmission.

by the looks of the meter, that appears to be a strong healthy tube.
you may need to examine that "brightener" to make sure that it is not a 1:1 ratio isolation transformer. that tube may have had a intermittant fil to cathode short.

Does this set use a 5U4 rectifier?
i would love to have this set to restore. sets like these are non-existant in this area.

That is a nice find.

That power transformer looks a little too small to do anything other than feed heaters. And I don't see a 5U4. Just be sure it's not a hot chassis. Or take the appropriate care if it is.
http://antiqueradio.org/art/Hoffman7...okInterior.jpg

No rectifier tube.

Phil Nelson

http://antiqueradio.org/art/Hoffman7M112TubeLayout.jpg

The set looks like a cross between a Hallicrafters, Crosley, with a little Motorola mixed in. It is a hot chassis. :scratch2:

I think it looks great! three IF stages, not two! Not as cheap as it could be. Insides look clean! Show us the chassis underneath when you can!

I replaced a couple of bad tubes and ran it up to about 100 volts on the variac (hey -- do what I say, not what I do :) ), when what to my wondering eyes should appear, but a bright green glow in the CRT neck.

http://antiqueradio.org/art/Hoffman7...nGlowInCRT.jpg

What the heck? The glow comes from what looks like some kind of schmutz on the tube element.

http://antiqueradio.org/art/Hoffman7...hmutzInCRT.jpg

This is without using the brightener (or should I say Britener?).

http://antiqueradio.org/art/Hoffman7M112Brightener.jpg

At roughly 100V the TV produces fine audio, which is mildly encouraging.

The ion trap magnet was originally far back against the tube base. I slid it forward out of curiosity and found that it has a slight effect on the green glow.

Never having seen a green glow outside of a magic eye tube -- this looks exactly the same shade, by the way -- I am most curious.

Phil Nelson

I seem to recall reading something about CRT makers using some type of marker for lining up the Ion trap, since this seems to be directly under the trap I wonder if that's what this is?
Obviously not gas because that would be purple and between the elements, this almost looks like it's something (phosphor?) applied to the outside of that part.

It definitely looks like a patch (or maybe stripe?) of something on the outside of that element. Possibly the same kind of green phosphor used in magic eye tubes or green CRTs?

For what it's worth (maybe nothing), the ion trap was originally not in that position. It was way back against the tube base and rotated about 30 degrees. Of course, someone might have monkeyed with it before, although the set doesn't show any obvious signs of tampering and the cover does have an AC interlock.

Phil Nelson

I'm guessing that green p-1 phosphor has been applied to the outside of the anode barrel to provide an indication of proper ion trap adjustment... minimize the scattered electrons = minimized green glow = max beam current down the gun to the screen. Just a WAG, however.

jr

That's pretty much what I recall reading, never saw one with it before though.
Maybe it's peculiar to this one brand, or rebuilder?

Curious how it can work being on the outside of the metal cylinder, unless it works by the cylinder becoming charged when the beam is hitting it instead of going down the center?

Phil, you never said if you got a raster or not?

Found this in a Rauland patent for a electrostatic focus CRT:
https://www.google.com/patents/US2627047

jr

Wow, that's interesting. I wonder if this could be a Rauland tube? I don't see any labeling on the base or what's visible of the neck.

The first time I tried the ion trap, I could clearly see the glow brighten or darken at various positions. (One practical drawback of this scheme is that the room needs to be nearly pitch black to see the green glow. I hadn't noticed it until I turned out the room lights in an effort to catch any glimmer on the screen.)

I don't have any hint of raster, or any sound of HV spooling up, although I'm not sure I can really hear that anymore.

I retried the set without the brightener, just for kicks, and guess what -- no green glow. I moved the ion trap around and suddenly there was a brilliant flash of green all the way around that tube element. Now there's no glow, with or without the brightener. So who knows, maybe that trace of green phosphor just made its last gasp, or for all I know there's a loose wire in the CRT cable.

Tomorrow I'll pull out the chassis and do some more sensible investigations, clean the tube pins & controls, etc. I'm wondering what sort of tuner this thing has, among other things.

Phil Nelson

Here is a quick peek under the 7M112 chassis. It's uncluttered and it should be easy to work on.

http://antiqueradio.org/art/Hoffman7...derChassis.jpg

The set has two selenium rectifiers and a sturdy (and clean!) turret-style tuner with 6J6 and 6BK7 tubes. The HV output section is also under the chassis and I removed its (solid steel) cage for this photo. The TV actually has 18 tubes including the CRT, even though only 15 are shown in the back-cover diagram.

Someone serviced this TV not too long ago. Notice the new resistor under the 1B3GT HV rectifier socket. I have exactly the same type of resistor in my parts boxes.

http://antiqueradio.org/art/Hoffman7M112HVSection.jpg

Here are a couple of other recent replacements:

http://antiqueradio.org/art/Hoffman7...placements.jpg

The electrolytic is piggybacked in parallel with a can electrolytic rather than taking the old cap out of circuit. :nono: I found another new electrolytic wired between two pins of the 6AH6 video amp. The red Big Chief cap looks like an older replacement. The original paper caps are a brand that I hadn't seen before: "Good-All Marbelite."

I made a couple of cursory checks and the B+ voltage seems reasonable. HV measures only 8.5KV, where that CRT normally wants something like 14KV.

The TV is still full of ancient electrolytics and paper caps, so I'm not going to burn a lot of time diagnosing specifics until it has been recapped. Lacking a good place to work, who knows when that will happen?

It's interesting to peek underneath, anyhow. Yes, it's an inexpensive, series-string set, but the factory wiring is tidy and the overall build quality looks decent. It's surprisingly sensitive, all things considered. When I first powered it up, it made very clear audio receiving a signal from my in-house transmitter, without anything connected to its antenna terminals.

Phil Nelson
Phil's Old Radios
http://antiqueradio.org/index.html

Looks like a Hoffmuntz. :yes:

This is a little different. These two items protrude through the rear panel as adjusters. The lower one looks like it would lever the core (?) up and down. The upper one terminates in something like a switch at the base of the coil. If these are HV adjusters, it's a new type to me.

http://antiqueradio.org/art/Hoffman7M112HVAdjuster.jpg

Today's puzzle: I see this little empty socket near the 3rd IF section. Wonder what goes here?

http://antiqueradio.org/art/Hoffman7...terySocket.jpg

There are no empty sockets elsewhere on the chassis, so presumably it's for some plug-in component, not a cable. Underneath, one terminal of the socket goes to ground and the other two are wired to a little network of resistors and (peaking?) coils that go to the 3rd IF stage and (through the big pink .1 cap) to the video amp.

http://antiqueradio.org/art/Hoffman7...onnections.jpg

The TV has loud and clear audio and the sound takeoff appears to be from pin 5 of the video amp, so presumably a signal is getting to that tube with nothing plugged into the mystery socket.

I don't know why you'd have a plug-in component here unless it's something optional or variable. Could this be some kind of local/distance thingie plugged in by the dealer in certain locales?

Phil Nelson

From the pix of the back of the set, it looks like the switch is a coarse position control and the funny screw thing is "width"... odd!

I have seen plugs like that used as test points for alignment.

Did the green glow return after sitting overnight?

jr

I would check the resistor that was replaced under the 1B3 socket. Maybe the wrong value was chosen and is starving the 1B3 filament.
The shaft the adjusts the flyback core gap is the width control. I would turn it fully clockwise, for now. The other shaft is for the horizontal centering.
Regarding the tuner: It could a Standard Coil. If the strips are in one piece, someone else made it!
BTW, the set is a parallel wired set. IDK, if the transformer has a winding for the damper tube or a secondary tap. :scratch2:

Your unidentified socket is between the 3rd Video IF tube and the video output tube. From Sam's 205-5 (see point A):

Looks like a test point to me. I will quit fretting over it. The schematic shows their 3-position range switch in the same neighborhood, so perhaps my local/distance guess wasn't completely insane.

Unfortunately, the green glow seems to be gone for good, no matter where you put the ion trap. It was fun to see, anyhow, even it seems a little gimmicky. I can see using it for a coarse setting, but I'd want to make the final adjustment looking at the screen.

The CRT is indeed a Rauland and its label has some instructions about using the green marker. Sooner or later, I'll loosen the retaining strap so that I can read the whole thing.

http://antiqueradio.org/art/Hoffman7M112CRTLabel.jpg

The tuner appears to have two strips per channel; it looks like the one in my Admiral console.

Thanks for the other advice. I'll check out that replacement resistor (and the replacement caps, for that matter).

Regards,

Phil Nelson

OK, I'm going to quit dissing this poor little $20 craigslist Hoffman.

http://antiqueradio.org/art/Hoffman7...rstPattern.jpg

http://antiqueradio.org/art/Hoffman7M112FirstImage.jpg

After replacing paper caps in the horizontal and sync sections, I decided to sub the 1B3GT and 6BQ6 tubes, out of superstition. (The others tested good, but you know.) I had also scrubbed the 1B3GT area with alcohol and given that resistor a good hard look.

When I went to play with the ion trap one last time -- bingo! -- the green glow was back, and within seconds I had a bright picture with terrific contrast and sharp focus. Don't ask me why someone put a brightener on this CRT. It looks as strong as a new one.

The second photo is receiving a cable broadcast with rabbit ears from my in-house transmitter, a decent real-world test of any old TV. A little blurry, but that's how all of my photos of live broadcasts seem to turn out.

Tomorrow I'll do some grown-up stuff like clean all of the pots and adjust the screen geometry, etc. It's fun to see it wake up, anyhow.

Phil Nelson

It looks like the CRT might be original. It sure looks good.
I worked on a Hoffman set, that was a year or two newer. It was real impressive, for a 21" table model.
A 6X9 speaker on one side, an 8" speaker on the other and push-pull audio output. It had that crazy Standard-Coil UHF-VHF tuner, with the two coil turrets, four stages of IF and large power transformer with two 5U4's.
Hoffman was really a high-end line at the time. This model had the easy-vision tinted safety glass.

Nice picture for such a basic, low-end-appearing TV set.

This is the first non-tinted Hoffman I have seen, not counting the one color set I have been in contact with.

The safety glass is tinted. I thought it was just grubby until I removed the glass for cleaning, but if you photograph it against white, the color jumps out. It's sort of a greenish amber.

http://antiqueradio.org/art/Hoffman7...afetyGlass.jpg

After recapping, the TV is working nicely except for a slight horizontal non-linearity and lack of width (see previous test pattern). The air-gap "width" adjuster mentioned earlier adjusts the HV output directly; I can get anything from 8KV to 10KV by turning it in or out, which makes the entire screen image grow or shrink. At 10KV, it's much too small and at 8KV (as low as I can go), it doesn't quite fill the mask horizontally.

I have the feeling that it would fill the screen if I could just correct the linearity, but the TV has no horizontal linearity adjuster. Here's the schematic for anyone who's curious.

http://antiqueradio.org/art/Hoffman7M112Schematic1.jpg
http://antiqueradio.org/art/Hoffman7M112Schematic2.jpg
http://antiqueradio.org/art/Hoffman7M112Schematic3.jpg

Perhaps there's a solution, but I'm not sure how much I can expect from this set. I wouldn't mind the minor non-linearity if it would just fill the dinged-danged mask.

Phil Nelson
Phil's Old Radios
http://antiqueradio.org/index.html